Liquid metal core transpactor elements for electromagnetic forming tools

ABSTRACT

Transpactor elements for electromagnetic forming tools comprising elastomeric members surrounding liquid metal cores are disclosed. When the transpactor elements are subjected to an intense varying magnetic field, the liquid metal cores deform. The elastomeric members transmit the deforming force to an associated workpiece causing it to deform into an adjacent die. When the magnetic field is removed, the elastomeric members restore the liquid metal cores to their original configurations. In order to protect the wearing surface of the transpactor elements, a replaceable elastomeric liner is mounted between the elastomeric member and the workpiece. In addition, the transpactor elements may include apparatus for maintaining the temperature of the liquid metal within a predetermined range. In one form, such apparatus cycles the liquid metal between a liquid metal resevoir and the elastomeric member. In an alternate form, such apparatus causes a liquid to flow through the elastomeric member to add heat to or remove heat from the liquid metal.

United States Patent [191 Larrimer, Jr. et al.

[ LIQUID METAL CORE TRANSPACTOR ELEMENTS FOR ELECTROMAGNETIC FORMING TOOLS [75] Inventors: Walter H. Larrimer, .Ir., Bellevue;

Donald L. Duncan, Seattle, both of Wash.

[73] Assignee: The Boeing Company, Seattle,

Wash.

[22] Filed: Feb. 27, 1974 [2l] Appl. No.: 446,491

[ June 10, 1975 Primary ExaminerRichard .l. Herbst Attorney, Agent, or Firm-Christensen. OConnor, Garrison & Havelka ABSTRACT Transpactor elements for electromagnetic forming tools comprising elastomeric members surrounding liquid metal cores are disclosed. When the transpactor elements are subjected to an intense varying magnetic field, the liquid metal cores deform. The elastomeric members transmit the deforming force to an associated workpiece causing it to deform into an adjacent die. When the magnetic field is removed, the elasto- [52] U.S. Cl 72/56; 72/63; [74/9 F meric members restore the liquid metal cores to their [5 l] Int. Cl 821d 26/14 original configurations. In order to protect the wearing [58] Field of Search 72/56, 63; 174/9 F; surface of the transpactor elements, a replaceable 29/42] M elastomeric liner is mounted between the elastomeric member and the workpiece. In addition, the transpac- [56] References Cited tor elements may include apparatus for maintaining UNITED STATES PATENTS the temperature of the liquid metal within a predeter- 730 847 (W903 Gilder et al 174/9 F mined range. In one form, such apparatus cycles the I 748927 2H930 Kramer [74/9 F liquid metal between a liquid metal resevoir and the [5:857 12/1963 Pf I I 72/56 elastomeric member. In an alternate form, such appa- 3,380,27l 4/l968 Habdas t 72/56 ratus causes a liquid to flow through the elastomeric 3,61 [.341 10/197! Craig et al .t 174/9 F member to add heat to or remove heat from the liquid 3.6l8,350 ll/l97l Larrimer. Jr. et al. 72/56 metal 3,688,535 9/l972 Keinarlen et al 72/56 22 Claims, 7 Drawing Flgures Fbn FE j fil/PPZ) f 1 LIQUID METAL CORE TRANSPACTOR ELEMENTS FOR ELECTROMAGNETIC FORMING TOOLS BACKGROUND OF THE INVENTION This invention is directed to electromagnetic forming tools and more particularly to transpactor elements for electromagnetic forming tools.

As discussed in US. Pat. No. 3,618,350 entitled Reusable Tooling for Electromagnetic Forming" issued Nov. 9, l971 to Walter H. Larrimer, Jr. et. al., and assigned to the assignee of this application, electromagnetic forming processes and apparatus have been used in the past to form metallic workpieces. In one form, electric currents are induced in the workpiece to be formed by an intense varying magnetic field. The repulsive interaction of the magnetic field created by the induced electrical currents with the magnetic field inducing the electrical currents causes a force sufficient to drive the workpiece against an adjacent die. As explained in the foregoing patent, this type of electromagnetic forming process is difficult to efficiently apply to metallic workpieces which have poor electrical current conduction characteristics and to nonmetallic workpieces. In an attempt to overcome this problem, the prior art has proposed the use of driver elements. However, prior to the invention described in the above noted patent, these elements become permanently de formed and, thus, were found difficult to remove from the formed workpiece. In an attempt to overcome this problem, the invention described in the above noted patent proposed reusable tooling (transpactor elements) for use in electromagnetic forming tools. Specifically, the above noted patent discloses a flexible, deformable, electrically conductive, material, such as a metallic structure formed of wire braid, wire mesh, metal fabric or the like, bonded to or embedded in an elastomeric material. When such a transpactor element is subjected to an intense varying magnetic field, the electrically conductive material forceably deforms and the elastomeric material transmits the deforming force to a workpiece, forming it into an adjacent die. Upon removal of the magnetic field, the elastomeric material restores itself and the metallic structure to their original configurations. While transpactor elements of the type described in the above noted patent have proven to be eminently satisfactory in operation, they remain subject to improvements. This invention is directed to such improvements.

More specifically, one of the problems with transpactor elements of the type described in the foregoing patent relates to the life of the elements. That is, it has been found that elements of the type described in the foregoing patent have a relatively short life, whereby the use of such elements is more expensive than desirable. More particularily, cyclindrical transpactor elements of the type described in the foregoing patent have been found to have a fatigue lives on the order of 25 energization cycles, depending upon how closely spaced the forming shots" are. The usual mode of failure has been found to be fatigue in the metallic material where the solder joint necessary to create the cylindrical shape, is located. While continuous weave braid conductors could possibly be used to eliminate this failure point, they cannot be optimized to the same degree as can a braid that is flattened, wrapped and silver soldered into a cylindrical shape.

It has also been found that the shot" rate or frequency of use of metallic material transpactor elements is limited by the temperature rise that occurs during such use because as the temperature rises the rate of elastomeric material degradation increases.

Therefore, it is an object of this invention to provide transpactor elements suitable for use in electromagnetic forming tools that are useful over an'extended number of energization cycles.

It is also an object of this invention to provide transpactor elements including temperature control means.

It is a further object of this invention to provide transpactor elements suitable for use in electromagnetic forming tools to form nonmetallic workpieces and metallic workpieces having poor current conduction characteristics.

As more fully described hereinafter, the invention overcomes the above noted problems of transpactor elements by providing elastomeric members which define an enclosed cavity. Located within the cavity is a liquid metal. While this basic structure overcomes the problems of short life noted above certain other problems exist which are also overcome by the invention. For example, over extended periods of use, the elastomeric material adjacent the workpiece becomes worn and breaks down, both because of use and because of the temperatures generated during use.

Thus, it is a further object of this invention to provide a liquid metal core transpactor element including means for extending the fatigue life of the elastomeric member.

It is a still further object of this invention to provide liquid metal core transpactor elements including means for controlling the temperature of the liquid metal core.

Finally, it is a more general objection of this invention to provide an electromagnetic forming tool including an improved transpactor element.

SUMMARY OF THE INVENTION In accordance with principles of this invention, transpactor elements suitable for use in electromagnetic forming tools are provided. The transpactor elements generally comprise an elastomeric member surrounding a liquid metal core. The elastomeric member and liquid metal core may be toroidal or planar, depending upon whether the workpiece to be formed is tubular or planar, or any other shape, as desired. Regardless of its shape, when a transpactor element formed in accordance with the invention is subjected to an intense varying magnetic field, such as the field created when a capacitor is rapidly discharged through a coil, the liquid metal core forceably deforms. The metal core deformation force is transmitted through the elastomeric member to the associated workpiece causing the workpiece to form or flow into an adjacent die.

In accordance with further principles of this invention, the liquid metal core is formed of a low melting point alloy having suitable electrical characteristics. Preferably, the low melting point alloy comprises at least two metals selected from the group consisting of: Cadimum, Indium, Bismuth, Lead and Tin. Cerrobend (Woods metal), Cerrolow 1 l7, Indalloy I8 or an Indium-Cadimum alloy having a 74-26 composition by weight are examples of such alloys. Moreover, the liquid metal core thickness is at least a skin depth thick at the frequency of energization.

In accordance with other principles of this invention, a removable and replaceable liner formed of an elastomeric material is located between the elastomeric member and the workpiece.

In accordance with still further principles of this invention, apparatus for controlling the temperature of the liquid metal core is also provided. In one form, the apparatus for controlling the temperature of the liquid metal core comprises: a reservoir of liquid metal; a pump for circulating the liquid metal between the reservoir and the elastomeric member; and temperature and flow control means for controlling the temperature of the liquid metal in the reservoir and the rate of flow of the circulating liquid metal. In an alternative form, the temperature control apparatus comprises: a tube having a good thermal conduction properties mounted in the elastomeric member and in direct contact with the liquid metal; a fluid, such as water, flowing through the tube; and, control means for controlling the temperature of the fluid with provision to alternately circulate hot water to maintain the liquid metal in a molten state and cold water to give optimum cooling when the frequency of use is high.

It will be appreciated from the foregoing brief summary that the invention provides new and improved transpactor elements suitable for use in electromagnetic forming tools. In their least complicated form, the transpactor elements of the invention merely comprise an elastomeric member with a cavity wherein a liquid metal is located. When the liquid metal is subjected to an intense varying magnetic field, it deforms. The deformation force is transferred via the elastomeric member to a workpiece whose configuration is to be changed. The transferred force drives the workpiece against a die to create the desired change. It has been found that the life time of this basic structure, when compared with the lifetime of structures of the type described in US. Pat. No. 3,618,350, referenced above, is better by a factor of at least seven. In order to further extend this lifetime, the invention provides for the inclusion of a replaceable elastomeric liner located between the elastomeric member and the workpiece. Lifetime of use is extended by the inclusion of such a liner because the greatest wear occurs where the transpactor element and the workpiece meet.

While a variety of liquid metals can be used to form the liquid metal core, low melting point alloys, as opposed to metals such as mercury or liquid sodium, are preferred in order to maintain hazard potential at a minimum. Because such alloys are solid at room temperature, they must be heated to their liquid state and maintained in such a state during use. With regard to the least complicated embodiments of this invention liquefaction is initially accomplished by heating the elements, such as in an oven. Liquefaction thereafter may be maintained in either of two ways. First, it may be maintained by employing a cycle rate at which the heat energy released will maintain the core alloy in a liquid state. Alternatively, if the cycle rate is too low, the transpactor elements must be periodically reheated.

The more complicated embodiments of the invention include the basic transpactor element plus apparatus for controlling the temperature of the liquid metal in order to more precisely maintain the temperature of the liquid metal within a desired range. In one form, the temperature of the liquid metal is controlled by circulating the metal between the cavity in the elastomeric member and a reservoir that is temperature controlled. In an alternate form, the temperature of the liquid metal is controlled by passing a fluid through a thermally conductive tube in good thermal contact with the metal. In either case, the apparatus is relatively uncomplicated, and yet will readily maintain the temperature of the liquid metal within a desired range.

It should be noted at this point, and will be appreciated by those skilled in the art, that it is desirable to maintain the temperature of the liquid metal within a predetermined range for several reasons. On the one hand, as discussed above, the temperature must be high enough to maintain the metal in a liquid state. On the other hand, it must be maintained low enough to limit the occurrance of undesirable effects. Among these undesirable effects are breakdown of the elastomeric member, weakening of the coil creating the intense varying magnetic field and increasing liquid metal core resistance.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing objects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is an exploded view illustrating part of an electromagnetic forming tool including a preferred embodiment of an expansion transpactor element formed in accordance with the invention;

FIG. 2 is a perspective view, partially broken away, of a transpactor element formed in accordance with the invention;

FIG. 3 is a cross-sectional view illustrating a preferred embodiment of a transpactor element formed in accordance with the invention mounted in an electromagnetic forming tool adapted to perform a swaging operation on tubular workpieces;

FIG. 4 is a cross-sectional view of an alternate embodiment of a transpactor element formed in accordance with the invention mounted in an electromagnetic forming tool adapted to form planar workpieces;

FIG. 5 is a perspective view, partially broken away, of a preferred embodiment of a transpactor element formed in accordance with the invention and suitable for use in an electromagnetic forming tool of the type illustrated in FIG. 4',

FIG. 6 is a plan view illustrating a transpactor element formed in accordance with the invention including one form of a control apparatus for controlling the temperature of the liquid metal held in the cavity of an elastomeric member; and,

FIG. 7 is a plan view illustrating a transpactor element formed in accordance with the invention including an alternate form of a control apparatus for controlling the temperature of the liquid metal held in the cavity of an elastomeric member.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a part of an electromagnetic forming tool 13 including a transpactor element 11 formed in accordance with the invention. The electromagnetic forming tool 13 comprises a die 15 formed of two sections 17 and 19 which, when brought together, form a circular toroid. The die 15 includes an annular forming groove 21. Concentrically located inside of the die is a tubular workpiece 23 which is adapted to be formed by the invention in the manner hereinafter described.

Concentrically located inside of the workpiece 23 is the transpactor element 11. More specifically, the transpactor element 11, as illustrated in FIG. 2, comprises an elastomeric member in the shape of a right circular toroid. Located inside, and defined by the elastostances. For example, it can comprise liquid sodium or mercury. However, these metals are not preferred because of their hazardous characteristics. Preferably, molten metals having melting points above room temperature (70C) and suitable electrical characteristics are used. Even more preferably, the liquid metal 28 is formed of one of several low melting point alloys (alloys that melt in the range 100F to 300F).'Some examples of such alloys and their composition by weight meric member 25 IS a cavity 27. The cavity 27 is also 10 are set forth in the following table.

TABLE I Resistivity Material Composition Melting Point pfl-cm Cerrobend Bismuth 50.0 1 S8F 42 (Woods Metal) Lead 26.7 Tin l3.3 Cadmium l0.0 Cerrolow ll? Bismuth 44.7 ll7F 37 Lead 22.6 Tin 8.3 Cadmium 5.3 Indium 19.1 lndalloy N0. l8 Indium 6L7 l43F 23 Bismuth 30.8 Cadmium 7.5 ln-Cd Alloy Indium 74.0 253F l3 Cadmium 26.0

in the shape of a right circular toroid and houses a liquid metal 28. Thus, the liquid metal forms the core" of the transpactor element 11.

Preferably an elastomeric sleeve or liner 29 concentrically surrounds the cylindrical outer periphery of the elastomeric member 25. The elastomeric annular sleeve or liner is adapted to be removed and replaced when it becomes degraded, due to abrasion by workpieces, to the point where it is no longer fit for use. Concentrically located inside the transpactor element 11 is a toroidal electromagnetic coil 31 supported on a cylindrical support member or mandrel 33.

In operation, the application of an intense varying electric current to the electromagnetic coil 31 induces a current in the liquid metal 28. The intense field of the coil produces a strong repulsion force on the current induced in the liquid metal 28. Since the current elements acted on by this repulsive force make up the liquid metal 28, the repulsive force acts to rapidly accelerate the liquid metal 28 away from the electromagnetic coil 31. The magnitude of the repulsive force is proportional to the currents flowing in the two circuits, i.e., the current flowing in the electromagnetic coil and the induced current flowing in the liquid metal. The magnitude of the induced current is, of course, dependent upon the electrical resistance of the liquid metal and the proximity of the liquid metal to the electromagnetic coil 31.

The repulsive force thusly created is transferred, through the elastomeric member 21 and the elastomeric sleeve 29, to the inner surface of the workpiece and drives and the workpiece 23 into the annular forming groove 21. If one such shot or energization cycle is inadequate to completely form the workpiece, one or more repeat cycles may be performed.

it will be appreciated by those skilled in the art and others that the current applied to the electromagnetic coil must be a rapidly varying intense electric current. One method of creating such a current is to discharge a capacitor through the electromagnetic coil.

The liquid metal 28 can comprise a variety of sub- All of the low melting point alloys set forth in Table I are solid at room temperature. Obivously, they must be in liquid form when the transpactor element of the invention is being used. Since the least complicated forms of the invention do not include a temperature control mechanism of the type illustrated in FIGS. 6 and 7, and hereinafter described, other methods of creating the desired liquefaction must be used. While the entire die, workpiece, transpactor element and electromagnetic coil could be placed in an environment wherein the temperature is adequately high, such a method is generally undesirable, because the rate of operation would have to be decreased in order to prevent the temperature of the liquid metal rising to a point wherein it rapidly degrades and destroys the elastomeric member. Rather, it is more desirable to first heat the transpactor to a liquefaction state in an oven. Thereafter, during use, liquefaction can be maintained in either of the two ways. First, use of the forming tool at low to moderate rates will generate enough heat to maintain liquefaction. Second, the transpactor can be periodically reheated in the oven. The latter method, of course, is only necessary if the shot rate is low.

While the resistance of low melting point alloys is substantially higher than is the resistance of braided transpactor elements of the type described in US. Pat. No. 3,618,350, equivalent workpiece deformation is created for the same amount of electrical power input. This result is attributable to two facts. First, the liquid metal has a larger cross section than does a heavy tin braided transpactor possessing adequate flexibility to be usable. Second, the liquid metal has essentially zero tensile strength when compared to a metal braid. Thus, it is easier to deform.

An additional parameter that is important and relates to the liquid metal core 28 is the thickness of the core. Specifically, it has been found that the liquid metal core, preferably, should be at least a skin depth thick at the electrical frequency of operation in order to efficiently contain the magnetic field of the coil thereby deriving maximum energy from the magnetic field. The

electrical frequency of operation or ringing frequency of course is determined by the electrical characteristics of the capacitor bank, the coil with its associated transpactor, and the transmission lines and switches. Skin depth is determined by this frequency and the resistivity of the liquid metal material involved, skin depth referring to the depth of the current paths. In any event, for an assumed ringing frequency of SKHz, the skin depth for: In-Cd is approximately 0. 100 inches; Indalloy No. 18 is approximately 0.130 inches; and, Cerrobend (Woods Metal) is approximately 0.180. The skin depth of Cerrolow 117 is slightly less than Cerrobend (Woods Metal).

A further important factor in determining optimum core thickness is the mass of the liquid metal which must be accelerated during use. For good efficiency, it is desirable to choose the mass such that the energy from the full first half of an energization cycle is coupled into the core before the transpactor element has moved across the slight gap separating it from the workpiece.

A variety of elastomeric materials can be used to form the elastomeric member 25 and the elastomeric sleeve 29. There are, however, some limitations which should be considered when a choice of materials is made. Specifically it has been found that during operation the temperature rise per energization cycle is approximately 20F. In view of this rise, high energization cycle rates have been found to raise the temperature of the liquid metal to 300F and above. Obviously, the elastomeric material must be adequate to retain its ability to return to its original configuration at the end of an energization cycle at such temperatures. Moreover, it should be able to handle an extended number of energization cycles (e.g. 200 or more) without undue wear at such temperatures. Further, the elastomeric material must not have a tendency to permanently deform under the conditions of use. In addition, other material characteristics relating to tear strength, hardness and resilience, should be considered. It has been found, through analysis and testing, that certain urethane rubber compounds have the qualities necessary for them to be used to form the elastomeric material. It should be noted, however, that the invention should not be construed as limited to these compounds because other compounds can also be used, as determined by the exact environment of use. Examples of urethane rubber compounds that have been found to be satisfactory are set forth in the following table.

(I) (34) Uralite 31 16A Uralite 31 16B The I-Iysol products noted in Table II are available from Hysol Division, The Dexter Corporation, 9640 Telstar Ave, El Monte, Cal. 91734. The Uralite products are available from Rezolin, Inc., 20701 Nordhoff St., Chatsworth, Cal. 91311. Of the components noted in Table II, the Hysol 2013/TM63B compound has been found to be a good compromise between hardness and tear strength. Even this material, however, tends to abraid and cut more readily than desirable at temperatures of normal use, i.e., generally 200F. and above.

It has been discovered that the life of the transpactor element 11 can be greatly extended by providing a replaceable elastomeric sleeve 29 located between the outer surface of the elastomeric member 25 and the workpiece 23.

FIG. 3 illustrates an alternate embodiment of a transpactor element of this invention embodied in an electromagnetic forming tool. Specifically, FIG. 3 illustrates an electromagnetic forming tool 41 adapted to form tubular structures by a swaging operation. The electromagnetic forming tool comprises a cylindrical housing 43 which supports the coil 47 hoop" stresses occurring during operation. The end pieces 45 of the cylindrical housing 43 provide end support for the coil 47 during operation. Concentrically arrayed on the inside of the inner periphery of the electromagnetic coil 47 is a toroidal-shaped transpactor element 49 formed in accordance with the invention. As with the transpactor element illustrated in FIG. 1, the transpactor element 49 illustrated in FIG. 3 comprises a cylindrical elastomeric member 51 enclosing a liquid metal 52 in a cylindrical cavity. Concentrically located inside of the elastomeric member 51 is a replaceable cylindrical sleeve or liner 53. The tubular workpiece 55 to be formed lies between the cylindrical sleeve 53 and a concentrically located cylindrical die 57. The die 57 includes an annular outer depression 59 which can take on any suitable cross-sectional form. To provide the desired acceleration gap, the tubular workpiece 55 is spaced from the cylindrical sleeve 53.

In operation, as with the embodiment of the invention illustrated in FIG. 1, when the electromagnetic coil 47 is energized in a suitable manner, the magnetic field it generates creates induced currents in the liquid metal. The induced currents, in turn, are repulsed by the field generated by the electromagnetic coils. The repulsion is such that an inwardly directed force is created. The inwardly directed force presses the workpiece 55 into the annular depression 59 in the die 57. Thus, an inwardly projection annular deformation is created in the workpiece.

Also illustrated in FIG. 3 is a power supply 61 connected through a switch 63 to the electromagnetic coil 47. Preferably, as discussed above, the power supply includes a capacitor that can be charged to a relatively high voltage level. When the switch 63 is closed, the capacitor is discharged. This discharge applys an intense varying current to the electromagnetic coil which, in turn, creates the intense magnetic field necessary to cause the desired repulsive force.

It will be noted from viewing FIGS. 1 and 3, and from the foregoing discussion, that the operation of both electromagnetic forming tools is identical. The only difference between the two tools is the end result. In one case (FIG. 1), the structure is such that the force is directed outwardly to form an outwardly projecting deformation in the tubular workpiece. In the other case (FIG. 3), the structure is such that the force is directed inwardly to form an inwardly projecting deformation in the tubular workpiece.

F IG. 4 is a cross sectional view illustrating a further alternate embodiment of a transpactor element 77 of this invention embodied in an electromagnetic forming tool 70. In this case, however, the electromagnetic forming tool is adapted to form sheet workpieces, as opposed to tubular workpieces.

The electromagnetic forming tool 70 illustrated in FIG. 4 comprises a base plate 71 supporting an upwardly projecting die form 73. Located above the die form 73 is the sheet workpiece 75 to be formed. Located above the sheet workpiece is the transpactor element 77. As better illustrated in FIG. 5, the transpactor element 77 comprises a pancake shaped elastomeric member 77 housing a liquid metal 79 in a suitable pancake shaped cavity. Located between the elastomeric member 77 and the workpiece 75 is a pancake shaped elastomeric liner 81, spaced from the workpiece by a narrow acceleration gap. Located above the elastomeric member 79, as viewed in FIG. 4, is a pancake shaped electromagnetic coil 83. The electromagnetic coil 83, the elastomeric member 77, and the elastomeric liner 81 are housed in a housing comprising a disk shaped member 85 and a cylindrical or ring member 87. The disk shaped member 85 supports the main coil reaction force and the ring member provides hoop support for the coil. The ring member 87 of the housing supports an attached restraining ring 89 which support the peripheral edge of the lower surface of the liner 81 and, thus, maintains the elastomeric liner and elastomeric member in contact with the electromagnetic coil of the housing.

In operation, when a switch 93, connecting a suitable power supply 91 to the electromagnetic coil 83 is closed, the electromagnetic coil 83 generates a magnetic field oriented such that is creates induced currents in the liquid metal. As with the previous embodiments of the invention, the induced currents, in turn, are repulsed by the field generated by the electromagnetic coil. This repulsion creates a force which is applied through the elastomeric member and liner to the workpiece 75 causing it to deform against the die form 73.

As with the previous embodiments of the invention, the elastomeric liner 81 is provided for replacement purposes. Hence, it can be eliminated, if desired. It should be noted at this point that the dimensions of the restraining ring 89 and the distance of repulsion must be such that the elastomeric member and/or the elastomeric liner, will return to their flat configurations subsequent to energization. This can be done by either affixing the elastomeric member and/or liner to the restraining ring 89, or by allowing the restraining ring 89 to extend inwardly far enough to prevent withdrawal of the elastomeric member and/or liner during use.

As discussed above, the temperature of the liquid metal forming the liquid metal core of various embodiments of the invention rises by a substantial amount each time an energization cycle or shot occurs. In order to prevent the temperature of the transpactor from rising to a point where it substantially degrades the elastomeric material, the shot rate must be kept low, at least when the transpactor element is formed in the manner previously described, i.e., when the transpactor element comprises a structure formed entirely of an elastomeric material housing a liquid metal, with or without a sleeve or liner. In some environments, a low repetition rate may be desired. However, it usually will be desirable to be able to operate the transpactor elements at high repetition rates. In addition, it will usually be desirable to provide transpactor elements that do not need to be heated in an oven prior to use. Or, more generally, it is desirable to provide transpactor elements including apparatus for controlling the temperature of the liquid metal core. As illustrated in FIGS. 6 and 7, and hereinafter described, the invention also provides transpactor elements that include such apparatus.

FIG. 6 illustrates a transpactor element 101 formed of a cylindrically shaped elastomeric member 103. L0 cated inside of the elastomeric member 103 is a cylindrical cavity 105 within which a liquid metal, such as low melting point alloy, 107 is housed. The cavity 105 is connected by an inlet tube 109 and an outlet tube 111 to a liquid metal reservoir 113. Preferably, the inlet and outlet tubes have poor thermal conduction properties. A pump 1 15 is connected such that when it is energized in the manner hereinafter described, it pumps liquid metal 107 from the reservoir 113 through the inlet tube 109 into the cavity 105 in the elastomeric member 103. This action forces any excess liquid metal in the cavity to return to the liquid metal reservoir 113 via the outlet tube 111.

A suitable electrical controller 117 is adapted to receive information from temperature sensors 104, 106, and 108 along signal wires 110, 112, and 114 related to the temperature of the liquid metal in the inlet and outlet tubes 109 and 111, and in the reservoir 113. Any suitable type of temperature sensing means, well known to those skilled in the art, such as thermisters and the like, can be utilized to provide this temperature information. In accordance with this information, the electrical controller 117 controls the pump 115, a heat exchanger 119 and a heater 116. The controller 117 is connected to the pump via a power conductor 120 so as to be able to control the rate of liquid metal flow through the cavity 105. In addition, the controller 117 is connected to the heat exchanger 119 and the heater 116 so as to be able to control the temperature of the liquid metal in the resevoir 113. The heat exchanger, for example, may comprise a cooling heat exchange coil 123 located in the reservoir 113 which is connected through inlet-outlet lines 122 and 124 to solenoid operated valves 121 which in turn adjust the amount of fluid flow through inlet-outlet lines 125 and 127 connected to a primary coolant supply (not shown). The cooling liquid or fluid may take on any suitable form; it may be water, for example. In accordance with the temperature information it receives, the controller 117 via the cooling liquid valves 12] controls the cooling of the liquid metal 107 by controlling the fluid flowing through the cooling heat exchange coil. Heating of the liquid metal in the reservoir 113 is provided by the heater 116 which may be electric and energized via a power conductor 118 running to the controller.

It will be appreciated that the controller 117 may take on a variety of forms. Since the specific form does not comprise a portion of this invention none will be described in detail. It should be noted, however, that the only basic requirement of the controller is that it control reservoir liquid metal temperature and rate of pumping 115 such that the temperature of the liquid metal flowing through the cavity 105 in the elastomeric member 103 is maintained within a predetermined temperature range.

An alternate embodiment of a transpactor element formed in accordance with the invention and including apparatus for maintaining the temperature of the liquid metal within a desired temperature range is illustrated in FIG. 7 and comprises a cylindrical elastomeric member 131 housing a cylindrical cavity 133 within which a liquid metal 135 is housed. In addition, a heat transfer tube 137 lies in the bottom of the cavity 133, as the cavity is viewed in FIG. 7. The heat transfer tube is broken (i.e., it does not define a complete circle) in order to keep it from preventing the elastomeric member 131 from expanding inwardly or outwardly during use. The tube 137 is adapted to carry a suitable heating or cooling fluid, such as water, for example. It should be noted that the shape or configuration, as well as the placement of, the heat transfer tube 137 may be varied in order to obtain the optimum result in different actual embodiments of the invention.

In order to control the temperature of the fluid in the heat transfer tube 137 and, thus, the temperature of the liquid metal 135, the heat transfer tube is connected at one end to the outlet of a solenoid operated inlet valve 155 and at the other end to the inlet ofa solenoid operated outlet valve 153. The inlet valve 155 has two inlets and the outlet valve 153 has two outlets. One inlet of the inlet valve 155 is connected to a fluid inlet pipe 139 and the other is connected to a pump outlet pipe 149. The pump outlet pipe 149 is connected to the outlet of a pump 145 mounted in a fluid reservoir 142. One outlet of the outlet valve 153 is connected to an outlet pipe 141 and the other is connected to a return pipe 147 that runs to the fluid reservoir 142.

A controller 151 receives temperature information from suitable temperature sensors mounted in the cylindrical cavity 133, the inlet to the circular tube 137 and the outlet from the circular tube 137 via signal lines 157, 159, and 161. In accordance with this temperature information, the controller controls: the position of the solenoid operated inlet and outlet valves 155 and 153 via power conductors 165 and 163; the pumping action of the pump 145 via power conductor 167; and, an electrical heater 144 via power conductor 169. More specifically, when it is desired to heat the liquid metal, the solenoid operated valves are adjusted by the controller 151 so as to cycle heated fluid 143 from the reservoir 142 through the heat transfer tube 137; the inlet and outlet pipes 139 and 141 being cutoff. ln addition, power is applied to the heater 144 and the pump 145 is energized. After the desired operating temperature of the heated fluid 143 in the reservoir 142 has been attained, power is supplied intermittently to the heater 144 by the controller 151 to maintain the reservoir temperature. In order to reduce the temperature of the liquid metal 135 after the temperature rise caused by a forming shot occurs, the inlet and outlet valves are opened by the controller 151 to the inlet and outlet pipes so that cooling fluid circulates through the heat transfer tube 137. Operation automatically proceeds in this cylic manner to maintain the temperature of the liquid metal in the desired range.

It should be noted at this point that while FIGS. 6 and 7 illustrate liquid metal control apparatus in combina tion with a cylindrical elastomeric member, the apparatus is equally suitable for use with other elastomeric member shapes, such as pancake (FIG. for exam ple.

It will be appreciated from the foregoing description that the invention provides transpactor elements having lifetimes of use substantially greater than the transpactor elements described in U.S. Pat. No. 3,618,350 and referenced above. Because of this improvement, the operative costs of electromagnetic forming roots using the invention are substantially reduced. In this regard, it has been found that the cost of forming using the invention is reduced by a factor of percent or more when compared with the cost of forming using transpactor elements of the type described in the foregoing patent.

As will be appreciated from the foregoing description, the invention can take on various forms. For example, it can be formed as an uncomplicated unitary structure. Alternatively, it can be more complicated and include temperature control apparatus. Also, it can include a replaceable sleeve or liner, if desired. These features all improve the flexibility of the invention whereby it is suitable for widespread use in the electromagnetic forming field, particularly the portion of that field directed to forming non-metallic items and metallic items having poor electrical conductity.

While preferred embodiments of the invention have been illustrated and described, it will be appreciated by those skilled in the art and others that various changes can be made therein without departing from the spirit and scope of the invention. Hence, the invention can be practiced otherwise than as specifically described herein.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A transpactor element suitable for use in an electromagnetic forming tool of the type wherein an electromagnetic coil lies adjacent to the transpactor element and the transpactor element creates a deforming force in response to the interaction between an electrical current induced in the transpactor element by the electromagnetic coil and the magnetic field generated by the electromagnetic coil, said transpactor element comprising:

an elastomeric member formed of an elastomeric material, said elastomeric member including an entirely enclosed internal cavity defined by at least a pair of walls spaced relatively close to one another; and, liquid metal core located in said internal cavity in said elastomeric member, said liquid metal core formed of a solid body comprising a low melting point alloy having a melting point above room temperature and electrical characteristics such that electrical currents are induced therein when said liquid metal core is in the presence of an externally generated magnetic field, said low melting point alloy comprising at least two metals selected from the group consisting of cadmium, indium, bismuth, lead and tin.

2. A transpactor element as claimed in claim 1, wherein the thickness of said liquid metal core is at least equal to skin depth at the frequency of said externally generated magnetic field.

3. A transpactor element as claimed in claim 2, including an elastomeric liner surrounding a predetermined portion of said elastomeric member.

4. A transpactor element as claimed in claim 3, wherein both said elastomeric member and said internal cavity are cylindrical in configuration.

5. A transpactor element as claimed in claim 4, wherein said elastomeric liner is cylindrical in configuration and surrounds the outer periphery of said cylindrical elastomeric member.

6. A transpactor element as claimed in claim 4, wherein said elastomeric liner is cylindrical in configuration and surrounds the inner periphery of said cylindrical elastomeric member.

7. A transpactor element as claimed in claim 3, wherein said elastomeric member and said internal cavity are pancake in configuration.

8. A transpactor element as claimed in claim 1, including apparatus for controlling the temperature of said liquid metal core.

9. A transpactor element as claimed in claim 8, wherein said apparatus for controlling the liquid metal core comprises:

a reservoir for holding a mass of the liquid metal forming said liquid metal core;

temperature control means for controlling the temperature of the mass of liquid metal in said reservoir; and,

cycling means for cycling liquid metal between said reservoir and said internal cavity.

10. A transpactor element as claimed in claim 8 wherein said apparatus for controlling the temperature of said liquid metal core comprises:

means for cycling a thermal conducting liquid through at least a portion of said internal cavity; and,

means for controlling the temperature of said thermal conducting liquid.

11. In an electromagnetic forming tool of the type wherein an electromagnetic coil lies adjacent to a transpactor element and the transpactor element creates a deforming force, adapted to form a workpiece into a die, in response to the interaction between an electrical current induced in the transpactor element by the electromagnetic coil and the magnetic field generated by the electromagnetic coil, the magnetic field generated by the electromagnetic coil being an intense varying magnetic field created by a rapid change in the current flowing through the electromagnetic coil and the like, the improvement comprising a liquid metal core transpactor element including:

an elastomeric member formed of an elastomeric material, said elastomeric member including an internal cavity; and,

a liquid metal core located in said internal cavity in said elastomeric member, said liquid metal core formed of a solid body comprising a low melting point alloy having a melting point above room temperature and electrical characteristics such that electrical currents are induced therein when said liquid metal core transpactor element is in the presence of the magnetic field generated by said electromagnetic coil, said low melting point alloy comprising at least two metals selected from the group consisting of cadmium, indium, bismuth, lead and tin.

12. The improvement claimed in claim 11, including an elastomeric liner surrounding a predetermined portion of said elastomeric member.

13. The improvement claimed in claim 13, wherein both said elastomeric member and said internal cavity are cylindrical in configuration.

14. The improvement claimed in claim 11, wherein said elastomeric member and said internal cavity are pancake in configuration.

15. The improvement claimed in claim 11, including apparatus for controlling the temperature of said liquid metal core.

16. The improvement claimed in claim 15, wherein said apparatus for controlling the liquid metal core comprises:

a reservoir for holding a mass of the liquid metal forming said liquid metal core;

temperature control means for controlling the temperature of the mass of liquid metal in said reservoir; and,

cycling means for cycling liquid metal between said reservoir and said internal cavity.

17. The improvement claimed in claim 16, wherein both said elastomeric member and said internal cavity are cylindrical in configuration.

18. The improvement claimed in claim 17, including an elastomeric liner surrounding a predetermined portion of said elastomeric member.

19. The improvement claimed in claim 16, wherein said elastomeric member and said internal cavity are pancake in configuration.

20. The improvement claimed in claim 15 wherein said apparatus for controlling the temperature of said liquid metal core comprises:

means for cycling a thermal conducting liquid through at least a portion of said internal cavity; and,

means for controlling the temperature of said thermal conducting liquid.

21. The improvement claimed in claim 20, wherein both said elastomeric member and said internal cavity are cylindrical in configuration.

22. The improvement claimed in claim 20, wherein said elastomeric member and said internal cavity are pancake in configuration. 

1. A TRANSPACTOR ELEMENT SUITABLE FOR USE IN AN ELECTROMAGNETIC FORMING TOOL OF THE TYPE WHEREIN AN ELECTROMAGNETIC COIL LIES ADJACENT TO THE TRANSPACTOR ELEMENT AND THE TRANSPACTOR ELEMENT CREATES A DEFORMING FORCE IN RESPONSE TO THE INTERACTION BETWEEN AN ELECTRICAL CURRENT INDUCED IN THE TRANSPACTOR ELEMENT BY THE ELECTROMAGNETIC COIL AND THE MAGNETIC FIELD GENERATED BY THE ELECTROMAGNETIC COIL, SAUD TRABSOACTIR EKEMENT COMPRISING: AN ELASTOMERIC MEMBER FORMED OF AN ELASTOMERIC MATERIAL, SAID ELASTOMERIC MEMER INCLUDING AN ENTIRELY ENCLOSED, INTERNAL CAVITY DEFINED BY AT LAST A PAIR OF WALLS SPACED RELATIVELY CLOSE TO ONE ANOTHER, AND,
 2. A transpactor element as claimed in claim 1, wherein the thickness of said liquid metal core is at least equal to skin depth at the frequency of said externally generated magnetic field.
 3. A transpactor element as claimed in claim 2, including an elastomeric liner surrounding a predetermined portion of said elastomeric member.
 4. A transpactor element as claimed in claim 3, wherein both said elastomeric member and said internal cavity are cylindrical in configuration.
 5. A transpactor element as claimed in claim 4, wherein said elastomeric liner is cylindrical in configuration and surrounds the outer periphery of said cylindrical elastomeric member.
 6. A transpactor element as claimed in claim 4, wherein said elastomeric liner is cylindrical in configuration and surrounds the inner periphery of said cylindrical elastomeric member.
 7. A transpactor element as claimed in claim 3, wherein said elastomeric member and said internal cavity are pancake in configuration.
 8. A transpactor element as claimed in claim 1, including apparatus for controlling the temperature of said liquid metal core.
 9. A transpactor element as claimed in claim 8, wherein said apparatus for controlling the liquid metal core comprises: a reservoir for holding a mass of the liquid metal forming said liquid metal core; temperature control means for controlling the temperature of the mass of liquid metal in said reservoir; and, cycling means for cycling liquid metal between said reservoir and said internal cavity.
 10. A transpactor element as claimed in claim 8 wherein said apparatus for controlling the temperature of said liquid metal core comprises: means for cycling a thermal conducting liquid through at least a portion of said internal cavity; and, means for controlling the temperature of said thermal conducting liquid.
 11. In an electromagnetic forming tool of the type wherein an electromagnetic coil lies adjacent to a transpactor element and the transpactor element creates a deforming force, adapted to form a workpiece into a die, in response to the interaction between an electrical current induced in the transpactor element by the electromagnetic coil and the magnetic field generated by the electromagnetic coil, the magnetic field generated by the electromagnetic coil being an intense varying magnetic field created by a rapid change in the current flowing through the electromagnetic coil and tHe like, the improvement comprising a liquid metal core transpactor element including: an elastomeric member formed of an elastomeric material, said elastomeric member including an internal cavity; and, a liquid metal core located in said internal cavity in said elastomeric member, said liquid metal core formed of a solid body comprising a low melting point alloy having a melting point above room temperature and electrical characteristics such that electrical currents are induced therein when said liquid metal core transpactor element is in the presence of the magnetic field generated by said electromagnetic coil, said low melting point alloy comprising at least two metals selected from the group consisting of cadmium, indium, bismuth, lead and tin.
 12. The improvement claimed in claim 11, including an elastomeric liner surrounding a predetermined portion of said elastomeric member.
 13. The improvement claimed in claim 13, wherein both said elastomeric member and said internal cavity are cylindrical in configuration.
 14. The improvement claimed in claim 11, wherein said elastomeric member and said internal cavity are pancake in configuration.
 15. The improvement claimed in claim 11, including apparatus for controlling the temperature of said liquid metal core.
 16. The improvement claimed in claim 15, wherein said apparatus for controlling the liquid metal core comprises: a reservoir for holding a mass of the liquid metal forming said liquid metal core; temperature control means for controlling the temperature of the mass of liquid metal in said reservoir; and, cycling means for cycling liquid metal between said reservoir and said internal cavity.
 17. The improvement claimed in claim 16, wherein both said elastomeric member and said internal cavity are cylindrical in configuration.
 18. The improvement claimed in claim 17, including an elastomeric liner surrounding a predetermined portion of said elastomeric member.
 19. The improvement claimed in claim 16, wherein said elastomeric member and said internal cavity are pancake in configuration.
 20. The improvement claimed in claim 15 wherein said apparatus for controlling the temperature of said liquid metal core comprises: means for cycling a thermal conducting liquid through at least a portion of said internal cavity; and, means for controlling the temperature of said thermal conducting liquid.
 21. The improvement claimed in claim 20, wherein both said elastomeric member and said internal cavity are cylindrical in configuration.
 22. The improvement claimed in claim 20, wherein said elastomeric member and said internal cavity are pancake in configuration. 